Compactin, a naturally occurring compound, is an effective inhibitor (Ki equals 1OnM) HMG-CoA reductase. We propose to investigate the structural basis for this inhibition. Fragments of compactin, compactin itself, and structural modification of these compounds will be synthesized. The inhibitory properties of these compounds will be studied to establish structural requirements for inhibition and to determine with what binding site of the enzyme each of the structural components of compactin interacts. A cyclopropanone analogue of mevaldic acid, an intermediate in the reduction of HMG-CoA, will be synthesized. Based on our previous studies with yeast aldehyde dehydrogenase, we expect cyclopropanone derivatives to be effective inhibitors of enzymes which act on aldehydes. An affinity column based on compactin will be prepared to facilitate the isolation of the yeast and mammalian HMG-CoA reductase. The reduction of HMG-CoA to mevalonic acid is a four electron reduction. We will investigate the mechanism of the reduction. The hypothesis will be tested that the yeast enzyme (tetramer) binds 4 NADP and 2 HMG-CoA molecules. These studies will initially be carried out with the yeast enzyme. Effective inhibitors will be tested with the mammalian enzyme. Their effect on cholesterol metabolism in vivo will also be determined. Through these studies, we hope to develop inhibitors of HMG-CoA reductase which will be pharmacologically useful, and derive general principles of enzyme inhibition.